AUBURN, Ala. — There are fourth-year seniors at Auburn who, before Saturday, had never beaten Alabama in the annual showdown known as the Iron Bowl.

These young men were still in high school during the famed Kick Six game here four years ago. They might have been middle-schoolers in 2010, when Cam Newton led the Tigers to victory in this game and then to the national title.

“The whole nation was watching tonight,” Cox added. “Everyone wants to see Bama lose. And we did that for the nation.”

The 26-14 upset victory for the No. 6 Tigers (10-2, 7-1 Southeastern Conference) placed them a win away from the College Football Playoff. Auburn will face No. 7 Georgia (11-1, 7-1) — a team it beat here, 40-17, a couple of weeks ago — next Saturday in Atlanta in the SEC championship game.

No. 1 Alabama dropped to 11-1, 7-1, and will wait anxiously in Tuscaloosa next weekend to see if the playoff selection committee and assorted upsets combine to grant the Crimson Tide their fourth straight appearance in the playoff.

Alabama’s run defense entered the game ranked No. 2 in the country, and it limited Auburn’s ground attack to 168 yards on 49 carries, or 3.4 yards per rush — nearly two yards below Auburn’s average entering the game.

The figure would have been lower had Auburn quarterback Jarrett Stidham, a sophomore, not scrambled with aplomb. Stidham rushed for 51 yards on 12 attempts, with a touchdown.

Auburn Coach Gus Malzahn called such plays “runaways” and referred to a defense that helped make them possible: “We caught them in man — opened up like the Red Sea.”

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Auburn running back Kerryon Johnson (21) after rushing 1 yard for a touchdown in the third quarter.CreditJohn Reed/USA Today Sports, via Reuters

Alabama safety Minkah Fitzpatrick, a junior, said Stidham’s footwork had taken the Crimson Tide (another way of saying Red Sea) by surprise. “This season he hasn’t run the ball a whole lot,” Fitzpatrick said, “and I think that they did a good job of adding that.”

Auburn’s hurry-up offense tore apart Alabama’s pass defense — the third-best in the country before the game — with Stidham finishing at 21 of 28 for 237 yards.

Rarely did Stidham throw without first faking a handoff, or hand off without faking a throw. Auburn’s first touchdown came on a characteristically nifty play, with running back Kerryon Johnson taking a direct snap, faking a handoff, taking a couple of steps forward and leaping to throw a bunny to the sophomore Nate Craig-Myers. In the fourth quarter, Stidham threw a 25-yard completion off a pitch from Johnson, who had again taken a direct snap.

Jalen Hurts, Alabama’s sophomore quarterback, was besieged by rushers and also harassed by the appropriately eagle-like screeches of the Jordan-Hare Stadium crowd. He completed 13 of 23 passes for 177 yards with one touchdown and added 80 yards on 17 rushes — almost as many carries as the Tide’s three talented running backs had together.

“We just didn’t do a good enough job in the passing game, but that is not just Jalen,” Coach Nick Saban said. “We didn’t have good enough protection, we didn’t have guys getting open.”

Alabama briefly seemed different at the beginning of the second half, when it put together one great drive — a screen pass and four rushes (none by Hurts) for 79 yards and a touchdown — and went up, 14-10.

Alabama’s offense was only 3 for 11 on third down, compared with Auburn’s 9 for 18.

Alabama entered the 82nd Iron Bowl superficially looking like the dominant team it had been in November of every season for the past decade.

But there was cause for concern. Hurts made fewer mistakes than he did in his rookie season, but the offense still depended on his legs. The defense, which suffered several injuries, was stout but not as opportunistic as usual: While Alabama had 10 non-offensive touchdowns (defense and special teams) in the 2015 season and an almost unthinkable 15 in the 2016 season, it entered, and departed, Saturday’s game with only one.

And the Crimson Tide’s undefeated record before Saturday may have required a grading curve. When Sunday’s Associated Press poll comes out, Auburn is likely to be only the second ranked opponent they have faced. To turn a familiar taunt against them: Alabama had not really played anybody.

A version of this article appears in print on , on Page SP1 of the New York edition with the headline: Auburn Stuns Alabama And Recasts Playoff Scene. Order Reprints | Today’s Paper | Subscribe